Voice over IP or VoIP is a type of advanced telephony that allows businesses to make calls using the Internet, by converting analog signals into digital data packets and transferring them through IP connections.

Usually, every data packet contains between 10 and 30 milliseconds of audio. However, since these connections use IP networks for communication, they must follow a transport protocol as UDP and TCP.

UDP (User Datagram Protocol) and TCP (Transmission Control Protocol) are two of the most widely used protocols for transferring data across the Internet. They govern how devices connect with each other, the reliability of their connection, and the way they exchange data.

Both these protocols are essential for networking, and each protocol has a unique role in a networking environment. That said, in terms of VoIP, these protocols are not the same. In this article, we will analyze TCP vs. UDP and see which one is better for VoIP solutions.

UDP vs. TCP for VoIP

VoIP networks use SIP (Session Initiation Protocol) for connecting with other VoIP devices (almost all devices use SIP for communication). Therefore, we must consider how both these protocols work in terms of SIP networks and VoIP environments.

Reliability vs. Speed

The TCP protocol is a ‘connection-oriented’ because it establishes a connection before starting data transfer. Between UDP and TCP, the latter places more focus on the accuracy of data packages received. TCP uses a system of acknowledgments to verify data packet delivery in IP connections.

Although accurate delivery of data packets is good, it comes with the expense of speed. The additional burden of sequence numbers, acknowledgment numbers, and checksum for error detection can slow connections down significantly.

TCP suffers from prolonged delays in limited bandwidth, which can is frustrating for people talking in real-time. For instance, in a sub-par connection, two speakers may hear each other after delays of a few seconds. However, in worse connections can extend to several seconds, making delays inconveniently long.

In contrast, the UDP protocol does not need logical connections for transferring information, so it can exchange data significantly faster. Although there are no prolonged delays, the lack of error detection in IPv4 means can introduce jitters during communication. However, these jitters are barely noticeable unless the connection is extremely poor.

Device Registration

TCP networks register devices at a small scale (i.e., a LAN network). However, a VoIP network may need to connect with thousands of devices of various types. VoIP connections contain SIP devices individual SIP phones, as well as other PBXs networks.

Therefore, these connections have to make SIP registrations where a SIP device (i.e., IP phone) informs a SIP server about its availability incoming and outgoing calls. SIP networks must do this every minute to ensure proper connections.

Since TCP forces connections to perform three-way handshakes, it can create a huge overhead for a VoIP solution when managing SIP devices. Although networks can tolerate this kind of overhead in a limited LAN environment, a VoIP solution may have thousands of devices trying to register at once. This kind of burden can make servers crash in little time.

Because the UDP protocol doesn’t need repetitive acknowledgments, VoIP networks are easier to manage on this protocol.

Real-Time Transmission and Call Quality

Once a VoIP network registers a phone, it needs a transport protocol to transfer data efficiently. A voice call is a conversation consisting of streams of packets. During a call, these packets are created, transmitted, and received, in real-time.

As mentioned before, retransmissions and acknowledgments in TCP voice call cause lag in voice calls. Although missing packets in TCP calls are less frequent than UDP, delays and pauses are more noticeable than missing packets. When someone is talking without a break, these delays during real-time transmissions easily add up to make the call quality worse.

Conclusion

Both TCP and UDP are essential for networking. However, since real-time data transmission is critical for VoIP solutions, a connectionless protocol (such as UDP) is more suitable for handling VoIP traffic. The UDP protocol stops the network from exerting unnecessary strain on SIP servers, and ensures optimal call-quality during SIP communication, making it the preferred protocol for VoIP connections.